Summary: Why Magnesium Diboride Is Not Described by Anisotropic Ginzburg-Landau Theory
A. E. Koshelev1
and A. A. Golubov2
1
Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
2
Faculty of Science and Technology, University of Twente, 7500 AE Enschede, The Netherlands
(Received 16 November 2003; published 12 March 2004)
It is well established that the superconductivity in the recently discovered superconducting compound
MgB2 resides in the quasi-two-dimensional band ( band) and three-dimensional band ( band). We
demonstrate that, due to such band structure, the anisotropic Ginzburg-Landau theory practically does
not have a region of applicability, because gradient expansion in the c direction breaks down. In the case
of a dirty band, we derive the simplest equations, which describe properties of such superconductors
near Tc, and explore some consequences of these equations.
DOI: 10.1103/PhysRevLett.92.107008 PACS numbers: 74.20.De, 74.70.Ad
Ginzburg-Landau (GL) theory is the most powerful
and widely used phenomenological theory of supercon-
ductivity (see, e.g., Refs. [1,2]). It describes practically all
known superconductors in the vicinity of transition tem-
perature. GL theory is fully microscopically justified and